The disclosed invention relates to honeycomb material having honeycomb cells of desired shape and being formed of a composite material, and to a method of making the honeycomb material. The honeycomb material is useful for spacecraft applications such as for wave guide arrays or structural members, as well as for submersibles and ground based antennas.
Typically, spacecraft utilize metallic honeycomb materials within structural elements. Of late, advanced composite materials other than metallic materials have begun to emerge. Since metallic honeycomb materials are typically made using a welding and/or expansion process, novel approaches are required to achieve similar structural materials using composite materials. A composite process gaining favor molds the honeycomb cells around forming rods and pins. See U.S. Pat. Nos. 5,981,025 and 5,443,884, for example. This known process is very labor intensive, and has severe limitations in the cell sizes and billet thicknesses achievable due to inherent limitations of manufacturing small thin long rods and pins. The practical limit in cell size is {fraction (3/16)} inch and the billet depth is 10-12 inches. There is an alternate process which molds an individual corrugated cell web, which is then secondarily bonded to an adjacent web to form the complete honeycomb cell structure. These constructions are typically of poor geometry, meaning that the webs are bonded to one another without internal support to the cells and as a result exhibit dimensional non-uniformity. This drastically affects the performance of the honeycomb core assembly when used structurally and even more so when used in wave guide array applications.
The method of the invention and the honeycomb material made thereby overcome the aforementioned limitations and drawbacks of the known methods and honeycomb materials. This is accomplished by the method of the invention of making a precision geometry honeycomb material having honeycomb cells of a desired cell shape and being formed of a composite material, wherein the method comprises molding a composite material in the cavity of a single-sided female mold which is configured to form a first web with a plurality of honeycomb cell portions of the desired cell shape in the web without necessitating the use of forming rods and pins as in the aforementioned known process. According to the invention, during molding the details of the cavity mold configuration of the single-sided female mold are captured to form the plurality of honeycomb cell portions in the composite material web by applying pressure to the composite material in the mold with an elastomeric pressure intensifier.
The elastomeric pressure intensifier, which can be reinforced with Graphite/Epoxy prepreg material, as required for rigidity and dimensional stability, applies pressure to the composite material in the mold is preferably configured to complement the cavity configuration of the single-sided female mold. For this purpose, according to the method the elastomeric pressure intensifier is formed by molding an elastomeric material in the single-sided female mold. In a disclosed embodiment, the pressure intensifier is a fluoroethylene polymer/polytetrafluorethylene faced elastomeric B-staged, calendered butyl rubber/silicone material.
Further, according to the method the molded first web is joined to a second web having a plurality of honeycomb cell portions which cooperate with the honeycomb cell portions in the first web to form a honeycomb material having honeycomb cells therein of the desired cell shape. In the disclosed embodiment, each of the webs has honeycomb cell portions which are half-cell portions. The joining includes accurately aligning the first and second webs with respect to each other in a fixture and adhesively bonding the facing webs to one another at opposing cell nodes located between the honeycomb cell portions of each web. The bonding fixture is configured to support the honeycomb cell portions of each of the webs for aligning and bonding the webs to one another. The improved method of the invention advantageously removes limitations of cell size and billet height (thickness). Cell sizes smaller than 0.100 inch are achievable in thicknesses greater than 24 inches. The shape of the cells in the disclosed embodiment is hexagonal but other shapes can be employed.
The honeycomb material produced by the method has a cell geometry with highly controlled dimensions, wherein the cell nodes of the webs are precisely aligned with respect to each and joined together to form the bonded connection such that the honeycomb material exhibits dimensional uniformity. Manufacturing costs are also lower with the invention as compared with rod/pin molding techniques. These attributes make the honeycomb material of the invention particularly useful in wave guide arrays and where structural designs call for honeycomb materials such as cores of complex geometry that are fashioned using computer numerical controlled machining of desired compound shapes.
These and other features and advantages of the present invention will become more apparent from the following detailed description of an embodiment of the invention taken with the accompanying drawings.